DE4430058B4 - Hydraulic drive system with a speed-controlled consumer and an electro-hydraulic control device - Google Patents

Abstract

hydraulic Drive system with a speed-controlled consumer (2) and an electro-hydraulic control device consisting from an external control loop (1) for speed control and a lower internal Control circuit (3) for pressure control, characterized in that the inner Control circuit (3) a hydraulic-mechanical feedback (13) of the consumer pressure wherein the hydraulic-mechanical feedback (13) in a force control valve (12) is arranged, which has a slide (14) for acting by a consumer pressure derived force (A ', B') and by a control force (K), wherein the force control valve (12) by a feedforward control (16) with stored control force map or stored control force characteristic is influenced.

Description

The The invention relates to a hydraulic drive system with a speed-controlled consumer and an electro-hydraulic control device consisting of an external control loop for speed control and a lower internal control loop for pressure control.

at Such a drive system, in which the outer loop the actual Speed control takes over, the task is assigned to the inner loop, the very low damping hydraulic To increase drives. For this purpose, the inner control loop consists of a setpoint-actual value reference junction, the one supplied by a speed controller of the outer loop and depending from a speed setpoint determined pressure setpoint with the actual value of the consumer pressure compares and the result passes a pressure regulator, which is controlled by a servo valve which is upstream of the consumer. To capture the Consumer pressure (actual value), a pressure sensor is used.

Such a generic drive system with a speed-controlled consumer and an electro-hydraulic control device having an outer control loop for speed control and a lower internal control loop for pressure control, which comprises a hydraulic-electrical feedback of the consumer pressure by means of pressure sensors, is from the DE 42 28 308 A1 known for a machine tool.

For use in mobile hydraulics, such a drive system is not suitable on the one hand the servo valve, the pressure regulator and the pressure sensor are very expensive components and on the other hand, these components The operating conditions occurring there did not grow in the long run are. For example, in the servo valve in addition to other filigree Components nozzles with only very small diameter and thin column present, which is light by external influences except Function can be set.

The DE 25 32 668 A1 shows a multi-stage pressure servo valve, which has a hydraulic-mechanical feedback of the consumer pressure by means of a pressure acted upon by the consumer pressure piston instead of a complex electro-hydraulic feedback of the consumer pressure.

Of the present invention is based on the object, a functionally reliable Hydraulic drive system of the type mentioned with reduced Effort and improved control features available too put.

These Task is inventively characterized solved, that the internal control loop a hydraulic-mechanical feedback of the consumer pressure wherein the hydraulic-mechanical feedback in a force control valve is arranged, which is a slide for loading by a force derived from consumer pressure and by a tax force having, wherein the force control valve by a pilot control with stored control force map or stored control force characteristic influenced is.

Opposite one hydraulic-electrical feedback of the Consumer pressure is the expense of a mechanical-hydraulic Return low. About that In addition, this direct return is a very good time behavior achieved, so that for the only weakly damped hydraulic consumers with the invention feedback a well-damped until Aperiodic behavior results. A low construction costs results from the arrangement of the hydraulic-mechanical feedback in a force control valve, the one slide to be acted upon by a consumer pressure having derived force and by a control force. Thus, one single is enough moved component, the consumer power and the control force against each other weigh and depending of which to regulate the consumer. For a cylinder with two chambers the slider is acted upon by a force coming from one of derived from the chamber pressures Pressure difference comes from. The for the control of the force control valve required control force depends both from the desired Speed of the consumer (target speed) as well from the high pressure in the drive system. This shows that the hydraulic-mechanical Repatriation already the influence of reasons one possible high efficiency fluctuating supply pressure (high pressure) largely compensates. On the other hand, the dependence is required Control force of the speed (target speed) clearly pronounced. According to the invention, it is provided that this Force control valve by a feedforward control with stored control force map or stored control force characteristic can be influenced. The Pilot control has opposite a scheme the advantage that at a setpoint change no control difference must be established before a manipulated variable change (i.e., no change the control force) takes place.

The control force can be applied for example by a control pressure. To this Purpose is favorable when the power control valve is preceded by a pressure control valve for generating the control pressure setpoint, wherein the upstream pressure control valve can be influenced by the pilot control with stored control force map or stored control force characteristic. The dynamics of this pressure control valve has no influence on the stability of the inner control loop. Therefore, it may have a much lower corner frequency than, for example, a servo valve in a generic hydraulic drive system.

in this connection is e.g. in a calculator the required control force (or the required control pressure) as a function of the required setpoint speed and the (measured) high pressure and the force control valve impressed. The Map or characteristic may e.g. stored in tabular form or be approximated by polynomials. Unless the requirements to the hydraulic drive system are low, the use is sufficient a control pressure characteristic, in which case, for example, only the influence the desired Speed up the hill considered the control pressure becomes.

at used in mobile drives (for example in excavators) Differential cylinders are the piston surfaces unequal size. For the inner one Control loop therefore results in a so-called all-pass behavior. In this case, the drive system moves in a sudden positive change in the Setpoint first in the negative direction and only then strives for the (positive) setpoint to. In order to avoid this, according to an advantageous development the invention proposed that at a load designed as a differential cylinder a weighted Hydraulic-mechanical feedback for both Chambers of the differential cylinder is provided. By weighting the consumer pressures of the differential cylinder is caused by the different sized piston surfaces effect compensated.

Around but to compensate for parameter variations and load changes it is advantageous if in the outer loop a speed controller is arranged, which is a setpoint-actual value comparison point is connected upstream and the summing point is followed, connected to the second input of the output of the pilot control is. The precontrol is thus supplemented by a return of the speed. there can in addition to the described reference variable control also a model following scheme can be used.

at hydraulic drive systems must be guaranteed as a basic requirement be that the high pressure generated by the pump is always sufficient to the required Speed of the consumer (this is true anyway for a A pump system, in which only one consumer is operated). On the other hand, it is desirable for efficiency considerations if the high pressure generated by the pump is not unnecessarily high is because then by closing the slide of the force control valve losses occur.

In Further development of the invention is therefore provided that the consumer connected to a pump with adjustable delivery volume, with a flow control or with a flow control with subordinate flow control in conjunction stands, and that one dependent on from the slide position of the force control valve effective additional regulator the flow control or the flow control with subordinate flow control is switched on.

It In this case, a specific slide opening is defined, e.g. 90% in which a certain high pressure is generated by the pump. falls below now the actual slide opening the defined value, the high pressure is reduced, exceeds she him, so the high pressure is increased. Are multiple consumers active, this relationship applies in each case to the consumer whose valve spool the most open is. Are all set values of the slide positions to zero or up set to a very low value, so is on a pressure control switched with low stand-by pressure.

The information about the slide position gives complete information about the pressure conditions at Consumer. In particular, if several consumers in the drive system are arranged, this is advantageous, because measuring the numerous load pressures with the associated problem (lack of fatigue and high cost of the sensors) is thus avoided. On the other hand, at the provided according to the invention measuring system in the force control valve on proven inexpensive products resorted become.

The described superimposed Control that evaluates the slide position of the force control valve ensures for one Pump pressure, on the one hand, the throttle losses are low and on the other hand the negative influences not caused by too low pressure manipulated variable restriction aufttreten.

Depending on the requirements of the behavior of the drive system, the detection of the slide position can be designed differently. In order to obtain a signal clearly assignable to the slide deflection, it proves to be advantageous if, for detecting the slide position, an inductive path measuring system is provided. With such a sensor, a continuous detection of the slide position is possible, so that the flow rate of the pump can be influenced by a steady regulator.

A simpler and very cost effective solution consists in detecting a slider position a switching sensor provided. With the help of a switching sensor so only detected whether the desired slide opening is reached, then with a regulator on the pump flow act.

Conveniently, at the force control valve of the control force, a spring force is in the opposite direction, wherein blocked in the absence of control force, the connections of the force control valve are. The spring force, which does not necessarily affect the functioning of the scheme is required, ensures a defined position of the force control valve in the absence of control force. This applies both when specifying a force setpoint value of zero as well as with a fault Failure of the control force.

Provided the control force is applied by a control pressure can, for Generating the control pressure to be used a pressure control valve which is supplied from the high pressure or a separate pressure network. It is also possible at pressure supply of the pressure control valve from the high pressure on constant pressure level for the pressure control valve by means of a pressure relief valve to produce.

According to one first embodiment is provided that parallel to the spring force Additional force is effective, by the pressure upstream of the force control valve is controllable. This makes it possible to clamp the slide of the force control valve hydraulically, so that the Natural frequency of the system control force - slider position very high is and opposite other natural frequencies of the drive system are neglected can. You get thus a force control valve with pure P - behavior, which is positive on the stability of the inner loop affects.

Conveniently, is to generate the control force to the supply line to the force control valve connected pressure control valve and to generate the additional power a connected to the supply line pressure relief valve intended.

The Hydraulic clamping described above is according to a advantageous development of the invention also before, if the Force control valve on both sides in each case against the force of a spring can be acted upon by a control force, for their generation in each case a provided to the supply line to the force control valve pressure control valve provided is. The springs center the slide of the force control valve in middle position.

Provided Consumers are provided, which have a large volume flow of pressure medium need is a high flow in the Force control valve and thus a large slide required whereby considerable flow forces occur. In this case, it is advantageous if the force control valve at least is formed in two stages. With direct controlling admission of the force control valve by control pressures and load pressures act these then on the small held slide of the first stage, the second larger slider downstream, which throttles the main pressure medium flow. Of the larger sliders thus acts as a power unit.

Becomes a force control valve with a directly operated slide for a Consumer who is under pressure even at standstill, e.g. a boom of an excavator, and the control pressure is switched off, Thus, the slider is not in the middle position, but is of the Load pressure shifted, so that pressure medium flow from the consumer can.

According to one further advantageous embodiment of the invention is proposed that the slider the force control valve from the load pressure of the associated consumer or a pressure derived therefrom can be acted upon and in one for acting on the slide provided line a in the middle position the slide is arranged the line shut-off valve. Thereby is achieved that the Load pressure of the consumer does not always act on the slide, although the force control valve has a simple design with only a few components in which the control pressures and those from the consumer press derived forces act directly on the slide. This is especially in safety engineering Advantages.

Further Advantages and details of the invention will be described with reference to the Figures schematically illustrated embodiment explained in more detail. there shows:

1 a speed control loop of the prior art,

2 a speed control loop with force control device,

3 a diagram of the dependence of the required control force on the high pressure,

4 a map to the dependence of the required control force of the target speed and the high pressure,

5 a timing chain with pilot control of the force control valve,

6 a speed control loop with pilot control,

7 a force control valve,

8th the control of a pump,

9 a force control valve in a first switching arrangement,

10 a force control valve in a second switching arrangement and

11 a force control valve in a third switching arrangement and

12 a variant of the shaft assembly according to 11 ,

In the 1 The speed control of the prior art shown shows a classic solution, as used for example for Gleichgangzylinder. It consists of an outer loop 1 for the speed control of a consumer 2 and a subordinate inner loop 3 for a pressure control.

A target SG for the desired speed of the consumer becomes a reference point 4 fed and compared there with an actual value IG, the speed of a sensor 5 is determined. Depending on the size of the deviation between the two values becomes a speed controller 6 acted upon, which generates a pressure setpoint SD depending on the control deviation, which a reference junction 7 is supplied. There is a comparison between the pressure setpoint SD and the actual pressure value ID of the consumer 2 instead of. The actual pressure value ID is determined by a pressure sensor 8th determined. Depending on the size of the deviation between the two values becomes a pressure regulator 9 acted upon, at the output of a servo valve 10 connected to the consumer 2 controls. The speed sensor 5 determines the actual speed, which is at the output of an integrator 11 results, which integrates the pressure proportional acceleration to the speed.

The outer loop 1 takes over the speed control. The inner loop 3 for pressure control has the task to increase the very low damping of hydraulic drives.

A such solution is for example for the Use in a construction machine unsuitable because the elements used, especially the servo valve, very expensive and vulnerable to those occurring in the mobile sector Are loads.

2 shows a speed control loop, instead of that of a pressure regulator 9 acted upon servo valve 10 and the pressure sensor 8th in the inner loop 3 a force control valve 12 is provided, which is a hydraulic-mechanical feedback 13 and a slider 14 having.

The hydraulic-mechanical feedback 13 has the great advantage that it has a very good time behavior. A weakly damped consumer (eg cylinders with D = 0.15) receives well damped to aperiodic behavior with such a feedback (eg D = 0.7). The amount of components for a hydraulic-mechanical feedback is low. The desired value (reference variable) is predetermined by a control force K, for example a control pressure, as given by one of the reference junction 7 upstream pressure control valve 15 is produced. The dynamics of this pressure control valve 15 has on the stability of the inner loop 3 no influence. Therefore, it may, for example, a lower corner frequency than the servo valve 10 of the prior art.

Unless the consumer 2 is designed as a differential cylinder, the recirculated consumer pressures, ie the pressures in the two chambers of the differential cylinder, according to the invention weighted, ie the influence of different sized piston surfaces of the differential cylinder on the consumer pressure is taken into account.

Next the steaming Effect equals the return of the consumer pressures at least partially the influence of the supply pressure, in applications in the field of mobile hydraulics for the sake of a maximum efficiency of the overall system (hydraulic drive system and internal combustion engine) fluctuates.

In 3 It is shown how the actual speed IG (ordinate) changes as a function of the high pressure P (abscissa) in the drive system with constant control force K (characteristic curve). The underlying feedback can thus largely reduce the influence of a fluctuating supply pressure, which is reflected in the approximately horizontal characteristics.

In 4 is the dependence of the required control force K (or the required control pressure) of the target speed SG and the high pressure P in the drive system shown as a map. The dependence of the required control force K on the target speed SG is clearly pronounced, the high-pressure influence, as already mentioned, low.

In the in 5 shown timing chain is the map off 4 as feedforward 16 for controlling the force control valve 12 upstream pressure control valve 15 used. Depending on the required speed SG (target speed) and the (measured) high pressure P in the drive system, the required control pressure is determined in an arithmetic unit, which is the force control valve 12 through the pressure control valve 15 is imprinted. The map can be stored, for example, in tabular form or be approximated by polynomials. For low requirements, the high pressure influence can also be neglected, so that the characteristic field becomes a characteristic.

The feedforward control 16 of the force control valve 12 has the advantage over a control that no control difference must be established at a setpoint change before a manipulated variable change (in this case: change the control force) takes place.

6 shows the integration of the pilot control 16 in the speed control in the form of a classic command value control. Here is the outer loop 1 arranged speed controller 6 a summation point 7a downstream, at the second input of the output of the pilot control 16 connected.

In 7 is a force control valve 12 shown as a switching symbol. The force control valve has the task to stabilize the internal control loop. For this purpose, in a differential cylinder as a consumer, the pressures in the two chambers of the differential cylinder are returned. Since the piston surfaces in the differential cylinder are unequal in size, the returned consumer pressures are weighted by the size of the piston surfaces. The at the slide of the force control valve 12 attacking forces are in 7 shown schematically. In addition to the two (always positive) opposing forces A 'and B', which are proportional to the chamber pressures of the differential cylinder, there is the control force K (both directions of force possible), through which the target value specification occurs The control force K can also be in the form of a control pressure , Another, not necessarily required for the operation of the force control valve force F, can be applied by a spring to ensure a defined rest position.

So far had been presupposed that of The pump of the drive system generated high pressure also sufficient is high so that the consumer reaches the required speed. The high pressure generated by the pump should not be unnecessarily high either be, otherwise by closing the slide of the force control valve undesirable losses. As a pump is usually adjustable in the delivery pump used, e.g. an axial piston pump whose pivot angle by a electrical signal can be given and then by a subordinate control loop is set.

According to one in the 8th illustrated embodiment of the invention is now provided that the slide opening of the force control valve for pump control of a pump 17 is used with. The setpoint SG for the speed of the consumer is a flow control 18 fed and converted there into a setpoint for the swivel angle of the (axial piston) pump, which at a summation 19 a signal is switched, which consists of a slider position of the force control valve evaluating additional controller 21 comes. In this way, a pump pressure is always provided, in which, on the one hand, the throttling losses become low, but on the other hand, the negative influences of a manipulated variable limitation caused by insufficient pressure do not occur.

In the 9 . 10 and 11 are different design options of the arrangement of the force control valve 12 demonstrated. In 9 is by an electrically controllable pressure control valve 22 the control force K applied (via a control pressure). With a force setpoint of size zero, the pressure regulating valve generates 22 a control pressure exactly that of a spring 23 generated force which is present at the position "hydraulic zero" of the slide. If there is no control pressure on the slide, the spring pushes the slide into a position in which all four connections (pressure, tank, two consumers) are closed and thus sets defined conditions at standstill and also in the event of failure of the pressure control valve 22 safe ("fail-save" behavior).

The pressure supply of the pressure regulating valve 22 can be done on the one hand from a separate pressure network or directly by high pressure. It is also conceivable to make the pressure supply from the high pressure line and a pressure relief valve, a constant pressure level for the pressure control valve 22 to create.

The Slider position is controlled by a switching or constantly working Sensor S detected and in the manner already described to control the High pressure used in the drive system.

10 shows a further embodiment, in which of the pressure control valve 22 generated control pressure not only against the spring 23 is present, but also against an opposing additional force, the pressure of a pressure relief valve 24 is applied. This pressure relief valve 24 is with respect to its nominal value of the applied high controlled pressure and is designed in this embodiment that halves the applied high pressure. This has the consequence that in the slide position "hydraulically zero" of the pressure control valve 22 applied pressure only by the spring 23 applied fraction of half high pressure different. Therefore, the slide between two hydraulic springs is clamped, so that the natural frequency of the system control force - slide position is very high and can be neglected compared to the other natural frequencies of the drive system (force control valve with pure P-behavior). This has a favorable effect on the stability of the inner control loop.

The hydraulic clamping is also given in one embodiment, as in 11 is shown. This is a pressure control valve for each direction of control force 22a respectively. 22b used. Two feathers 23a and 23b ensure centering of the slide in the middle position.

The switching arrangement according to 12 differs from the switching arrangement 11 in that in the lines branched off from the lines led to the consumer and to the bearing surfaces of the slide of the force control valve 12 are guided, each a valve 24a respectively. 24b is arranged with a blocking and a flow position. The valve 24a respectively. 24b is always in blocking position when the slider of the force control valve is in the middle position with the control pressure switched off.

On this way is prevented at a consumer under pressure even at a standstill (for example a boom of an excavator, which has a holding pressure of about 100 bar requires) the slide is moved under load and pressure medium flows out of the consumer. This is safety advantage. Unintentional movements of the consumer are prevented.

Claims (13)

Hydraulic drive system with a speed-regulated consumer ( 2 ) and an electro-hydraulic control device, consisting of an outer control loop ( 1 ) for speed control and a lower internal control loop ( 3 ) for pressure control, characterized in that the inner control loop ( 3 ) a hydraulic-mechanical feedback ( 13 ) of the consumer pressure, wherein the hydraulic-mechanical feedback ( 13 ) in a force control valve ( 12 ), which is a slide ( 14 ) for application by a pressure derived from the consumer pressure force (A ', B') and by a control force (K), wherein the force control valve ( 12 ) by a pilot control ( 16 ) is influenced with stored control force map or stored control force characteristic. Hydraulic drive system according to claim 1, characterized in that the force control valve ( 12 ) a pressure regulating valve ( 15 ) is connected upstream for generating a control pressure setpoint, wherein the upstream pressure regulating valve ( 15 ) by the pilot control ( 16 ) is influenced with stored control force map or stored control force characteristic. Hydraulic drive system according to claim 1 or 2, wherein the consumer ( 2 ) is designed as a differential cylinder, characterized in that a weighted hydraulic-mechanical feedback ( 13 ) is provided for both chambers of the differential cylinder. Hydraulic drive system according to one of Claims 1 to 3, characterized in that in the outer control circuit ( 1 ) a speed controller ( 6 ), to which a setpoint-actual value comparison point ( 4 ) is preceded and a summation point ( 7a ) is connected downstream, at whose second input the output of the pilot control ( 16 ) connected. Hydraulic drive system according to one of Claims 1 to 4, characterized in that the consumer ( 2 ) to a pump ( 17 ) is connected with adjustable delivery volume, which with a flow control ( 18 ) or with a flow control ( 18 ) with subordinate flow control ( 20 ) and in that a function of the slide position of the force control valve ( 12 ) Effective auxiliary regulator ( 21 ) of the flow control ( 18 ) or the flow control ( 18 ) with subordinate flow control ( 20 ) is switched on. Hydraulic drive system according to claim 5, characterized characterized in that Detecting the slide position an inductive measuring system is provided. Hydraulic drive system according to claim 5, characterized characterized in that Detecting the slider position a shift sensor is provided. Hydraulic drive system according to one of claims 1 to 7, characterized in that on the force control valve ( 12 ) of the control force (K) a spring force (F) is in the opposite direction, wherein in the absence of control force (K), the connections (P, T, A, B) of the force control valve ( 12 ) are locked. Hydraulic drive system according to claim 8, characterized in that parallel to the spring force (F) an additional force is effective, by the Pressure upstream of the force control valve ( 12 ) is controllable. Hydraulic drive system according to Claim 9, characterized in that, to generate the control force (K), a supply line to the force control valve ( 12 ) connected pressure control valve ( 22 ) and for generating the additional force a connected to the supply line pressure relief valve ( 24 ) is provided. Hydraulic drive system according to claim 8, characterized in that the force control valve ( 12 ) on both sides in each case against the force of a spring ( 23a . 23b ) by a control force (K) can be acted upon, for their generation in each case one to the supply line to the force control valve ( 12 ) connected pressure control valve ( 22a . 22b ) is provided. Hydraulic drive system according to one of claims 1 to 12, characterized in that the force control valve ( 12 ) is formed at least two stages. Hydraulic drive system according to one of claims 1 to 12, characterized in that the slide ( 14 ) of the force control valve ( 12 ) from the load pressure of the associated consumer or a pressure derived therefrom can be acted upon and in a for acting on the slide ( 14 ) provided line in the middle position of the slide ( 14 ) the valve shut-off valve ( 24a . 24b ) is arranged.